The pore diameter of porous ceramics materials generally depends on the size of the primary particles. Conventionally, when larger pore diameter is required, a compound which disappears in sintering (e.g., organic resins) is mixed with the starting ceramics powder, and the mixture is then sintered. In this method, however, a defatting device which removes a gas generating from such a compound disappearing in sintering is required, and thus the production cost becomes high. Moreover, when the specific gravity of the compound disappearing in sintering is different from that of the ceramics powder, it is difficult to mix these ingredients uniformly so that porous ceramics materials having a uniform pore diameter cannot obtained.
Hydroxyapatite is similar in nature to inorganic main components of bones and teeth and has excellent biocompatibility, so it has been utilized as a ceramic bioimplant material exemplified by artificial tooth roots, artificial bones, etc. Tricalcium phosphate is also known to have equally good biocompatibility.
What is interesting about hydroxyapatite is that it also has good characteristics for use as a packing in chromatography and it has been used in separating and purifying biomaterials such as proteins, enzymes, nucleic acids, etc. In recent years, products of porous spherical hydroxyapatite having good separating ability have been developed and commercialized; this type of hydroxyapatite holds much promise for us in a broad range of applications.
One method for producing a packing from hydroxyapatite comprises synthesizing a hydroxyapatite slurry by a wet method, granulating the slurry by a suitable method such as spray drying, and shaping the particles into a desired form. The particles produced by this method have a disadvantage in that because of the weak binding of primary particles, the secondary particles which are made up of such primary particles are low in strength and are not highly durable. The strength of the particles can be increased by heat treating them at elevated temperatures (.gtoreq.700.degree. C.) so that the primary particles are sintered. This method is effective in improving the strength of the particles but disadvantageously the ability of the treated particles to adsorb acidic proteins such as bovine serum albumin (BSA) is lowered.